Hydrolytic degritter

ABSTRACT

The present invention relates to improving the results of anaerobic digestion of organic waste especially animal manure such as chicken manure by removing the grit in the waste. by digesting the waste in a slurry at a temperature of 50 degrees C. or more for a period of time sufficient for the grit to settle out of the slurry.

COPYRIGHT NOTICE

A portion of the disclosure of this patent contains material that is subject to copyright protection. The copyright owner has no objection to the reproduction by anyone of the patent document or the patent disclosure as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a system and method for the degritting of waste, such as animal waste, in a hydrolytic system. In particular, it relates to waste digestion at incubation temperatures which causes grit to settle out of the incubation slurry.

2. Description of Related Art

The anaerobic digestion of organic material such as sewage sludge, municipal waste, industrial waste, forest waste, agricultural waste, and especially animal waste is the fermentation of such material by bacteria in the absence of oxygen. The benefit of such digestion of waste material includes the stabilization of waste, odor control, solid reduction, energy production in the form of methane gas, elimination or reduction of pathogens, making the waste more environmentally neutral, production of a nutrient source, and the like. Generally, it has been used in many large scale treatments of animal wastes to control the disposal problem associated with such waste.

Animal feed, in particular, poultry feed, typically has a large amount of insoluble grit material such as limestone, sands or shells material added to improve the feed for food grinding in the gizzard and to supplement calcium to the animal. The insoluble grit becomes a large problem when delivered to an anaerobic digester for biogas production. The grit can clog up the feed lines and fill up the internal space of the digester. It tends to be abrasive as well and can easily damage equipment. The removal of such grit is highly desirable.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to the discovery that grit can easily and cost effectively be removed from waste material such as poultry waste. The process involves hot water and waste being combined and mixed at elevated temperatures in a tank allowing all the grit to settle to the bottom of the tank for separation.

Accordingly, in one embodiment, the present invention relates to a method of separating grit from organic waste comprising:

-   -   a) adding raw organic waste to a tank fitted with a mixing         apparatus;     -   b) adding water to the organic waste in the tank to obtain an         8-12% slurry mixture;     -   c) maintaining the temperature of the slurry at a temperature of         at least about 50° C. while mixing the contents of the tank with         the mixing apparatus for a period sufficient for the grit to         settle to the bottom of the tank; and     -   d) separating the settled grit from the remaining slurry in the         tank.

In another embodiment, the present invention relates to a system for separating grit from a low solids raw organic waste slurry comprising:

-   -   a) a tank equipped with a mixing apparatus and containing the         slurry;     -   b) a device for removing grit that has settled to the bottom of         the tank selected from the group comprising a pump or a device         to bleed or remove the grit from the bottom of the tank; and     -   c) a device for maintaining the slurry at a temperature of at         least about 50° C. for a period of time sufficient for the grit         to settle out from the slurry.

In another embodiment the present invention is a system which further comprises a device for performing anaerobic digestion on the slurry in the tank after the grit is removed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a hydrolytic degritter of the present invention.

FIG. 2 is a view of the hydrolytic degritter in a biogas/fertilizer production system.

DETAILED DESCRIPTION OF THE INVENTION

While this invention is susceptible to embodiment in many different forms, there is shown in the drawings and will herein be described in detail specific embodiments, with the understanding that the present disclosure of such embodiments is to he considered as an example of the principles and not intended to limit the invention to the specific embodiments shown and described. In the description below, like reference numerals are used to describe the same, similar or corresponding parts in the several views of the drawings. This detailed description defines the meaning of the terms used herein and specifically describes embodiments in order for those skilled in the art to practice the invention.

DEFINITIONS

The terms “about” and “essentially” mean ±10 percent.

The terms “a” or “an”, as used herein, are defined as one or as more than one. The term “plurality”, as used herein, is defined as two or as more than two. The term “another”, as used herein, is defined as at least a second or more. The terms “including” and/or “having”, as used herein, are defined as comprising (i.e., open language). The term “coupled”, as used herein, is defined as connected, although not necessarily directly, and not necessarily mechanically.

The term “comprising” is not intended to limit inventions to only claiming the present invention with such comprising language. Any invention using the term comprising could be separated into one or more claims using “consisting” or “consisting of” claim language and is so intended.

Reference throughout this document to “one embodiment”, “certain embodiments”, and “an embodiment” or similar terms means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of such phrases or in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments without limitation.

The term “or” as used herein is to be interpreted as an inclusive or meaning any one or any combination. Therefore, “A, B or C” means any of the following: “A; B; C; A and B; A and C; B and C; A, B and C”. An exception to this definition will occur only when a combination of elements, functions, steps or acts are in some way inherently mutually exclusive.

The drawings featured in the figures are for the purpose of illustrating certain convenient embodiments of the present invention, and are not to be considered as limitation thereto. Term “means” preceding a present participle of an operation indicates a desired function for which there is one or more embodiments, i.e., one or more methods, devices, or apparatuses for achieving the desired function and that one skilled in the art could select from these or their equivalent in view of the disclosure herein and use of the term “means” is not intended to be limiting.

As used herein the term “grit” refers to insoluble matter that exists within organic waste. This especially includes the solid material found in animal waste such as described above. The term “organic waste” refers to any of the waste type materials described above which would be used in an anaerobic digestion system and containing grit. In one embodiment the organic waste is animal manure. In another embodiment it is chicken manure.

As used herein the term “tank” refers to a tank designed for holding organic waste and mixing at an elevated temperature. The tank can be made of any material such as stainless steel and in one embodiment, the tank is insulated to better hold the elevated temperature. The tank is fitting on the interior with a mixing apparatus to keep the contents of the tank mixing during the process of the invention. One skilled in the art could choose an appropriate mixing apparatus. Since the grit needs to be removed and eventually ends up on the bottom of the tank after the process, the tank can be fitted with a pump to remove the grit or remaining slurry, or with a bottom drain such as conical area, to remove the grit by bleeding off the grit. The degritted slurry is transferred by pump into the anaerobic digester.

The tank or system is emptied, typically daily, for the second batch of hydrolysis.

The method of the present invention involves adding the organic waste such as animal manure (chicken manure) to the tank. Water is added to the tank to obtain a lower solids slurry mixture. In general one skilled in the art can obtain the optimum percentage of solids, and thus the proper amount of water based on the weight of the manure added by simple testing of the process. In one embodiment the percent solids is 8% to 12% on a weight/weight basis. In other embodiments it can be 12% or less solids and can in some circumstances be higher than 12%. In general, the degritter process takes about a day, however, it depends on the severity of grit.

The contents of the tank need to be kept at a temperature of at least about 50° C. during the method of the present invention and as such the tank must also be fitted with a device for heating the contents and holding at that temperature. The tank can also be insulated. The water and/or manure can be preheated to that temperature before addition to the tank or can be heated in the tank after addition. Both analog and digital temperature control devices are within the skill in the art. In one embodiment the temperature is kept within about 50 to about 60° C. for a period sufficient to settle out essentially all the grit from the slurry. The sufficient time as used herein will vary depending on the organic material and ambient conditions, the size of the tank, and the like, but in one embodiment the time is about 18 to 24 hours. One skilled in the art could readily determine the amount of time based on the teachings herein and with minimal experimentation.

Once the slurry is degritted, it can be delivered to an anaerobic digester for productivity of biogas and fertilizer. Also, it can be further digested in a novel secondary solid. SECONDARY SOLID-PHASE DIGESTION FOR BIOGAS SEMI-SOLID PRODUCTION of a patent application filed of even date herewith.

Now referring to the figures, the following FIG. 1 depicts an embodiment of the hydrolytic degritter system of the present invention. In this view insulated tank 1 is shown with slurry 2 which is made from the addition of water 3 and manure 4 from containers/pipelines/faucets etc. Once the proper low solids slurry is formed, it is heated or kept heated by heater 5 and then kept in a. state of constant missing using mixer 6. In this embodiment an 8-12% solids content slurry is utilized.

FIG. 1 shows the process with grit 10 settling out at the bottom of tank 1. In reality, the solids would settle out after the process but is shown in this manner for convenience. In this embodiment grit 10 can be removed from tank 1 by bleeding the grit into container 15. The grit 10 in container 15 can be washed and that washing returned to the tank. The tank slurry minus the grit is transferred 7 to an anaerobic digester for production of biogas and fertilized over a period of 5-10 days. Though one skilled in the art can determine optimum times.

FIG. 2 shows the hydrolytic degritter in a system for digesting the manure into biogas and solid material slurry which can be used for fertilizer and other uses. The slurry material is transferred to the primary anaerobic digester 11. The slurry is digested for about 5-10 days or as needed to produce biogas 12 and a solid slurry about 2-5% solids 13. The solids 13 are delivered to a secondary solid phase digester 14 for further biogas production and a semi-solid slurry which can be utilized as fertilizer 16 and a leachate 17.

Those skilled in the art to which the present invention pertains may make modifications resulting in other embodiments employing principles of the present invention without departing from its spirit or characteristics, particularly upon considering the foregoing teachings. Accordingly, the described embodiments are to be considered in all respects only as illustrative, and not restrictive, and the scope of the present invention is, therefore, indicated by the appended claims rather than by the foregoing description or drawings. consequently, while the present invention has been described with reference to particular embodiments, modifications of structure, sequence, materials and the like apparent to those skilled in the art still fall within the scope of the invention as claimed by the applicant. 

What is claimed is:
 1. A method of separating grit from organic waste comprising: a) adding raw organic waste to a tank fitted with a mixing apparatus; b) adding water to the organic waste in the tank to obtain a slurry mixture; c) maintaining the temperature of the slurry at a temperature of at least about 50° C. while mixing the contents of the tank with the mixing apparatus for a period sufficient for the grit to settle to the bottom of the tank and d) separating the settled grit from the remaining slurry in the tank.
 2. The method according to claim 1 wherein the temperature is maintained at about 50° C. to about 70° C.
 3. The method according to claim 1 wherein the slurry has about 8% to 12% solids.
 4. The method according to claim 1 wherein the contents are mixed and incubated for about 18 to 24 hours.
 5. The method according to claim 1 wherein the grit is removed by at least one of pumping or bleeding off from the bottom of the tank.
 6. The method according to claim 1 wherein after the grit is removed, the remaining mixture in the tank is pumped to an anaerobic digester for digestion.
 7. The method according to claim 1 wherein the organic raw waste is raw animal manure.
 8. The method according to claim 7 wherein the manure is chicken manure.
 9. A system for separating grit from a low solids raw organic waste slurry comprising: a) a tank equipped with a mixing apparatus and containing the slurry; b) a device for removing grit that has settled to the bottom of the tank selected from the group comprising a pump or a device to bleed or remove the grit from the bottom of the tank; and c) a device for maintaining the slurry at a temperature of at least about 50° C. for a period of time sufficient for the grit to settle out from the slurry.
 10. The system which further comprises a device for performing anaerobic digestion on the slurry in the tank after the grit is removed. 